[kmcdonou]

I'm burning-in my upgraded MPX3 and installed a set of tubes that I had used in the amp the day before--Sylvania 12sn7gta as driver, two Sylvania 12sn7gts as outputs. When I plugged them in and turned on my source, I could barely hear the volume, even if I turned it up ridiculously high. I assume I have a tube that has burned out or is close to burning out.

How do I know which one it is? The gt tubes are chrome tops so I can't really see the filaments very well. I was in a hurry and my amp is tucked under a shelf, so I didn't examine the gta tube very long. Do I need to simply swap out one tube at a time until I find the culprit? This is my first time for a tube to go bad.

 

[EdipisReks]

if you don't have a tube tester, swapping them around is probably going to be the only way to tell for sure. if the volume is equally low in both channels, however, i bet it's the gain tube that is the culprit.

 

[kmcdonou]

Ah, that is a nice tip about the left and right channels. So if one is quieter than the other, then that tube is going out. I think both were quiet, so you are probably right that the gain tube is burned out.

 

[sacd lover]

Quote:

Originally Posted by kmcdonou I'm burning-in my upgraded MPX3 and installed a set of tubes that I had used in the amp the day before--Sylvania 12sn7gta as driver, two Sylvania 12sn7gts as outputs. When I plugged them in and turned on my source, I could barely hear the volume, even if I turned it up ridiculously high. I assume I have a tube that has burned out or is close to burning out. How do I know which one it is? The gt tubes are chrome tops so I can't really see the filaments very well. I was in a hurry and my amp is tucked under a shelf, so I didn't examine the gta tube very long. Do I need to simply swap out one tube at a time until I find the culprit? This is my first time for a tube to go bad.

Did you have the 12 volt filament supply plugged in but forget to turn on the high voltage supply?

 

[kmcdonou]

I don't have a 12v supply switch. I thought I remember you describing this too, but I called Mikhail and he said all I needed to do was plug in the 12v power supply. I was listening to music last night with just the 12v power supply plugged in and it sounded fine. I hope I didn't misunderstand Mikhail and there is a switch somewhere, although I don't know where it could be.

When the 12v supply is plugged in a red light comes on.

 

[sacd lover]

Quote:

Originally Posted by kmcdonou I don't have a 12v supply switch. I thought I remember you describing this too, but I called Mikhail and he said all I needed to do was plug in the 12v power supply. I was listening to music last night with just the 12v power supply plugged in and it sounded fine. I hope I didn't misunderstand Mikhail and there is a switch somewhere, although I don't know where it could be. When the 12v supply is plugged in a red light comes on.

My amp was the first one he did so he probably found a better way to implement the 12 volt tubes. I have two power supplies. I have to plug in the 12 volt filament supply first(I dont have a switch either I plug/unplug the power supply at the IEC connection). I leave the 12 volt supply connected to the amp all the time.The green LED I have blinks until the 12 volt power supply is fully charged and operational. Then you hit the normal power switch that turns on the high voltage supply. I have plugged in the 12 volt supply and then forgot to turn on the high voltage supply and had what you described occur. If you go in the wrong order you can get the same results.